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Post-mortem Interval (ALGOR MORTIS (BODY COOLING) (Cooling (retarded by:
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Post-mortem Interval
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Supravital reactions
- Reaction of tissues on post-mortem stimulation
- Mechanical and electrical excitability of the muscle
- pharmacological excitability of the iris.
- Mechanical excitability of the muscle
-hitting the muscle with a reflex hammer (Biceps-brachi, quadriceps).
-Three phases:
a) First phase: contraction of the whole muscle (propagated excitation): hit the lower third of the thigh 4-5 fingers breath above the knee cap and a contraction can be seen up to 1.5-2.5 hours post-mortem
b) Second phase: strong and typically reversible spasm is noted up to five hours post-mortem.
c) Third phase: weak muscular spasm can be obtained up to 24 hours post-mortem.
- ELECTRICAL EXCITABILITY OF THE MUSCLE:
-Rosenthal found that the orbicularis oculi muscle remained excitable for long periods.
-Lasts longer in acute deaths and well nourished individuals
-impulses of 30mA with 10 ms duration at a repetition rate of 50 per second are applied.
-Six degrees of muscle contraction:
Grade VI:Muscles of the same side of the face are contracted, seen up to 3.5 hours
Grade V: Muscles of orbital and frontal region are contracted, up to 4.5 h
Grade IV: contraction is restricted to the eye, up to 5.5 h
Grade III: contraction is seen on the upper eyelid, up to 8 h
Grade II: contraction is restricted to the length of muscle between the electrodes, up to 10.5h
Grade I: weak contraction is obtained below the electrodes, up to 13.5 h
- Pharmacological excitability of the iris:
-iris muscle can be reactive to electrical and pharmacological stimulation for longer periods than skeletal muscle.
-0.5 mls of 1% atropine (Enlargement, 4-20 h), Pilocarpine (Constriction, 4-20 h), epinephrine or norepinephrine (Enlargement, 14-46 h) or 5% acetylcholine (Constriction, 14-46 h) can be injected in the subconjunctival sac.
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Vitreous Potassium {K+}
- Autolysis proceeds faster in blood than in Vitreous Humour (VH) due to its isolated and confined topography
- VH is the fluid compartment mainly studied for late post-mortem chemical changes.
- There is a linear relationship between potassium concentration and time after death up to 120 hours, but the 95% confidence limits are ± 22 hours
- Factors influencing the post-mortem rise of VH potassium:
Temperature
Chronic illness
Urea retention (100 mg/dl)
Insect activity
- theory behind estimating the PMI with the help of insects are very simple: since insects arrive on the body soon after death, estimating the age of the insects will also lead to an estimation of the time of death.
- First arrives is the blow- flies or Calliphoridae
- Calliphoridae will lay their eggs on the body, especially around the natural orifices such as the nose, eyes, ears, anus, penis and vagina.
- Flesh flies deposit larvae instead.
- it takes between one week and two weeks from the egg to the pupae stage.
- exact time depends on the species and the temperature in the surroundings.
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- time of death
- estimating the time of death are based on different approaches:
1) ante-mortem changes ( gastric contents)
2) Post-mortem changes (cooling, rigor mortis, hypostasis, etc.)
- Stomach contents:
-Used to estimate time based on state of digestion.
-Stomach emptying is governed by variables:
nature of the meal (fatty food retards stomach emptying)
presence of alcohol and its amount
state of health of the deceased
emotional state of the deceased
Head injury, for example, completely abolishes stomach emptying.